The present invention relates generally to a clamping apparatus, and more particularly to a mold clamping apparatus used for an injection molding machine.
Typically, a mold clamping device has upper and lower mold halves for movement relative to each other to define a mold cavity by closure of the mold halves. The device is controlled so that a predetermined force clamping the mold halves is obtained and sustained for a predetermined time.
A toggle-type clamping arrangement is typically used for moving one of the mold halves relative to the other along a longitudinal axis of the device. In an exemplary arrangement, one end of each of a pair of links in a toggle linkage is supported for rotation on pivot pins. One of the pivot pins is secured to a movable unit having an upper mold half while the other is secured to a stationary unit having a lower mold half. The other end of each of the pair of links is supported for rotation on an intermediate pivot pin, which is connected operatively with a drive capable of moving the intermediate pin in a direction transverse to the longitudinal axis. For, example, a ball screw is used in the drive mechanism. With this construction, the transverse movement of the intermediate pivot pin allows the movable unit to move up and down (in the longitudinal direction) relative to the stationary unit.
In this clamping device using such a linkage, in order to support a relatively large clamping force, a radial needle bearing having an excellent load resistance is preferably used as a bearing mounted, for example, between a link and pivot pin. However, there are cases where thrust is generated because the rollers skew between the outer and inner rings of the bearing, which may damage components such as the bearing, the link or the ball screw.
Hence, it is an object of the present invention to provide a clamping apparatus with high reliability capable of preventing such damage of the components.
It is another object of the present invention to provide a radial needle bearing that serves to prevent such damage effectively.
To achieve the above object, a clamping apparatus of the present invention includes upper and lower platens; one or more tiebars for connecting the upper and lower platens; an intermediate platen provided between the upper and lower platens for movement relative to and along the tiebars. Upper and lower mold halves are provided on the upper and intermediate platens, respectively. A linkage is provided for connecting the lower and intermediate platens. A drive mechanism drives the linkage so that the lower platen is moved relative to the intermediate platen, so that the upper mold half on the upper platen is moved relative to the lower mold half on the intermediate plate. The linkage includes upper and lower links connected with each other for rotation on an intermediate shaft. The upper link is pivotably supported on a first shaft fixed on the intermediate platen. The lower link is pivotably supported on a second shaft fixed on the lower platen. The intermediate shaft is operatively connected with the drive mechanism so that the mechanism transmits a driving force to the linkage. A set of radial needle bearing and thrust bearing is used for at least one of the intermediate, first and second shafts.
According to the apparatus, where the thrust may be generated when the rollers of the radial needle bearing in the linkage skew, the trust can be applied to the trust bearing, so that the components of the linkage are prevented from being damaged.
A radial needle bearing of the present invention includes a set of needle rollers each having spherical axial ends; and holding members facing said axial ends of the rollers for restraining against axial movement of the rollers. The holding members are separated from outer and inner rings of the bearing. Even if the rollers skew, the rollers can be brought into contact with the holding members through the spherical ends. With this construction, a stress concentration does not occur as in the case where needle rollers each having cylindrical or flat ends are used and, as a result, the rollers that skew may be brought into contact with the holding members through the edges. This has the advantage to improve the fatigue life of the holding members.